The present invention relates to a fiberscopic device for the inspection of the interior sections of a construction, such as a machine, vessel, piping and the like, and to a method for using the same, and in particular, has application to the inspection of the hot sections, such as the combustion chambers or cans, of jet engines.
While the present invention is described hereinbelow in the context of one inspection procedure for a particular model of jet engine, it will be appreciated by those skilled in the art that this description is illustrative only, and that the invention disclosed herein is neither limited to such types of inspections nor only to inspections of jet engines; rather, the teachings disclosed herein have many applications. Further, while for ease of description the device is described as being useful for inspecting machine interiors, it should be understood that it is not so limited, and may be used to inspect many types of constructions or devices not admitting of easy visual inspection.
It has long been desirable to inspect the interior sections of constructions, such as vessels, piping or certain types of machinery, including jet engines, to examine for defects such as coking, cracking, wear, burning, etc. To avoid the need to disassemble the engine, which itself suffers from several drawbacks, various other methods have been proposed to inspect the engine interior while the engine is assembled, or even still mounted on the wing of an aircraft. In one known method, the engine is wrapped with a radiation-sensitive film, and a radioactive source is inserted into the engine to expose the film from within the engine. While this method is usually adequate to locate gross defects in the engine's condition, it is not sufficiently sensitive to reveal, for example, cracks or burn spots which while they appear minor at the time of inspection, perhaps due to the insensitivity of this method, might perhaps warrant maintenance at that time, or even worse, lead to more serious defects if left untreated. Further, even when this method is able, for example, to locate a crack, because of its imprecision it is typically incapable of discerning the length of the crack.
Accordingly, fiberscopic devices, which also have known medical applications, have been used to inspect the interior of jet engines, either or alone or as an adjunct to a radiation-sensitive film technique. Examples of known fiberscope devices are disclosed in U.S. Pat. Nos. 3,583,393 and 3,788,304 assigned to Olympus Optical Co., Ltd. of Tokyo, Japan, which are herein incorporated by reference. Typically, a fiberscopic device includes an elongated tube, or probe, with light transmitting and fiber optical systems along its length to illuminate an interior section to be inspected and transmit an image back to an eyepiece through which the operator can view the image.
A disadvantage of the known fiberscopic designs when used to inspect a machine has been the inability to control the movement of the fiberscope probe within the interior of the machine to enable a more thorough inspection, for example, into adjacent interior sections of the machine which are not themselves accessible from the exterior of the machine. For example, in the inspection of a particular aircraft jet engine, the model JT8D manufactured by Pratt & Whitney Aircraft, a division of United Technologies, the known fiberscopic devices are useful in inspecting the two combustion chambers, or cans, (#4 and #7) which are accessible from the exterior of the engine via the ignitor ports of the engine. Only with a great deal of operator manipulation, if at all, is it possible to extend the fiberscope probe through a crossover tube connecting either the #4 or #7 can with an adjacent can. (It will be appreciated that a JT8D engine comprises nine combustion cans). Thus, the condition of the two cans, i.e., the #4 and #7 cans, which are capable of visual inspection with the known fiberscopic devices has been used in conjunction with other inspection techniques to predict the condition of the cans which cannot be reached with the fiberscope probe for a visual inspection. Obviously, a device capable of permitting a thorough visual inspection of all of the combustion cans of this or any other engine, and for that matter, other interior sections of other constructions or machines which are not readily accessible from the exterior, would be highly desirable.
Accordingly, it is among the objects of the present invention to provide an improved fiberscopic inspection device which enables an operator to control and manipulate the fiberscope probe accurately while extended into the interior of a construction. It is another of the objects of the invention to enable the inspection of adjacent interior sections, including those to which access cannot readily be had from the exterior of the construction.